Methods and Devices for Producing Biodiesel and Products Obtained Therefrom

ABSTRACT

Methods and devices for economically producing a purified biodiesel product from feedstocks. Some embodiments of the methods comprise using at least one of a crude feedstock pretreatment process and a free fatty acid refining process prior to transesterification and the formation of crude biodiesel and glycerin. The crude biodiesel is then subjected to at least one biodiesel refining process which, in conjunction with feedstock pretreatment and free fatty acid refining produces a purified biodiesel product that meets multiple commercial specifications. A wide variety of feedstocks may be used to make biodiesel that otherwise would not meet the same commercial specifications, including corn oil, used cooking oil, poultry fats, fatty acid distillates, pennycress oil, and algal oils. The combination of feedstock refining and biodiesel refining processes is necessary to reduce problems associated with feedstocks having waxes, high free fatty acid levels, unacceptable color, high unsaponifiables levels, and high sulfur levels.

This application is a continuation of U.S. application Ser. No.14/897,174 filed on Dec. 9, 2015 which is a National Phase filing ofinternational application number PCT/US2014/041708 filed Jun. 10, 2014which is based upon U.S. Provisional Application Ser. No. 61/833,504filed Jun. 11, 2013, the complete disclosures of which are herebyexpressly incorporated by this reference.

FIELD OF THE INVENTION

The present invention generally relates to processing low-costfeedstocks into high quality biodiesel that meets multiple commercialbiodiesel specifications.

BACKGROUND

Biodiesel is a renewable, clean-burning petroleum diesel replacementthat enhances independence from imported petroleum, reduces greenhousegas emissions, supports agriculture and rural economies, and createsjobs.

While biodiesel provides many benefits, biodiesel production must beeconomical in order to maintain supply of the advanced biofuel.Producers must adapt to changing market conditions with new processesfor converting low-cost feedstocks while meeting stringent productquality specifications.

Biodiesel finished product quality standards have evolved over recentyears. Currently, to ensure product consistency and protect theconsumer, biodiesel quality is regulated according to various commercialstandards, including ASTM D6751, EN 14214, CAN/CGSB 3.524, and numerouscustomer-specific specifications. The aforementioned specificationsrequire biodiesel to be produced with tight tolerances for manyproperties, including flash point, residual alcohol, water and sediment,kinematic viscosity, sulfated ash, oxidation stability, sulfur, copperstrip corrosion, cetane number, cloud point, carbon residue, AcidNumber, cold soak filterability, monoglycerides, total and freeglycerin, phosphorous, 90% distillation temperature, calcium andmagnesium, sodium and potassium, particulate contamination, and estercontent. The most recent revision of ASTM D6751, D6751-12, introducedmultiple biodiesel grades with different limits for Cold Soak Filtrationtest time and monoglyceride content, further increasing the importanceof these two properties for customer acceptance of biodiesel.

As specifications for biodiesel become more rigorous than anticipated byearlier designers of production processes and as demand for lower costand non-food feedstocks increases, biodiesel producers have an urgentneed to improve their production processes to allow the use of newand/or low-cost feedstocks in order to compete and remain economicallyviable. However, low cost feedstocks contain a variety of low levelimpurities that can negatively impact biodiesel quality according to theaforementioned commercial specifications.

Corn oil is an example of a promising lower cost, non-food biodieselfeedstock that contains impurities that prevent traditional biodieselplants from using it to produce biodiesel that meets all commercialspecifications. In 2005, the U.S. produced 42 percent of the world'scorn. As of September 2012, the United States had the nameplate capacityto produce approximately 14 billion gallons of ethanol in 211operational ethanol plants. As of only a few years ago, marketconditions changed allowing it to be profitable for ethanol producers toseparate corn oil from the byproducts of ethanol production. Todemonstrate the potential volume of corn oil that could be recoveredfrom ethanol plants, a 100 MGPY ethanol plant is theoretically able toproduce 7 million gallons of corn oil annually.

Much of the corn oil that has been recovered to date has been sold foruse in animal feeds and for industrial uses since it poses a number ofchallenges for biodiesel production. Corn oil contains wax compoundsthat cause biodiesel to fail the Cold Soak Filtration test in ASTM D6751when processed in traditional biodiesel production processes. It hasproven difficult to remove these waxes from the finished biodieselproduct, in part because of their solubility in biodiesel alkyl estersacross a wide temperature range. Waxes can be partially removed usingcold filtration technology or other winterization techniques. Anembodiment of the invention disclosed herein successfully removes a vastmajority of these waxes so as to efficiently meet ASTM D6751specification requirements.

Corn oil from ethanol plants also contains elevated free fatty acid(FFA) content. The FFA content of this corn oil may be between about 4and 15 wt %. In general, high FFA feedstocks are difficult to processinto biodiesel by base-catalyzed transesterification because the FFAsare converted to soaps leading to undesirable processing consequences(e.g., emulsion formation and increased catalyst costs), yield losses,and production rate downturns. The invention disclosed herein allowsnearly any feedstock to be processed, regardless of its initial FFAcontent. As described below in detail, the invention includes multipleembodiments for reducing FFA in the feedstocks (i.e., deacidifying them)prior to transesterification, including conversion to soaps followed byphysical removal, physical removal by distillation, and/or chemicalconversion by esterification with an alcohol, such as methanol, ethanol,or glycerol.

In some cases even after feedstock pretreatment with an FFA reductionprocess, residual FFA levels can still remain higher than desirable fortraditional biodiesel production, which can result in higher Acid Numbervalues in the finished biodiesel. This is of particular concern forbiodiesel produced from feedstocks such as corn oil and some fatty aciddistillates. When corn oil, corn oil biodiesel, and fatty aciddistillates (along with biodiesel produced therefrom) are analyzed forAcid Number with ASTM D664 Method B, they reveal a second inflectionpoint in the titration curve caused by compounds that are neutralizedafter the free fatty acids. This additional inflection point causes thefeedstock to exhibit an Acid Number greater than would be predicted byits true FFA content, and this Acid Number increase can be imparted tothe resulting biodiesel. One of the embodiments of the inventiondisclosed herein efficiently reduces the quantities of both FFAs and thecompounds that cause the second inflection point such that the finishedbiodiesel more easily and more predictably meets commercial biodieselspecifications for Acid Number.

In addition to having higher FFA levels than conventional commodity fatsand oils, lower cost, non-food feedstocks for biodiesel are often muchdarker in color and higher in sulfur content. In traditional productionprocesses, the darker color and a significant portion of the sulfurcontent are largely imparted to the finished biodiesel, which can createbarriers to meeting commercial specifications and to customer acceptancein general. For example, corn oil sourced from ethanol processescustomarily retains a deep red color. The red color of the resultingbiodiesel gives the appearance of fuel that has been dyed, which is theestablished governmental regulatory method to clearly advisewholesalers, retailers and consumers that a diesel product is foroff-road use only. Red-dyed diesel fuel has critical tax implicationsand is therefore strictly regulated. In commercial distribution ofbiodiesel made from ethanol-sourced corn oil, fuel retailers andend-users have expressed deep concern about using this fuel for on-roadapplications, even to the point of refusing to accept the product. It isimportant to overcome this failure of market acceptance. Our researchindicates that this red coloration can be reduced to acceptable orange,yellow, or even clear colorations depending on the embodiment of thisinvention that is chosen for processing the feedstock and purifying thebiodiesel. For example, some biodiesel filter aids may reduce theintensity of the red color, but only to a limited extent. It is costlyand inefficient to sufficiently eliminate the red color by use ofbiodiesel filter aids alone. However, removing free fatty acids from thecorn oil by distillation and then purifying the eventual biodiesel withfilter aids will produce biodiesel with a commercially acceptable color.

Similarly, certain filter aids can reduce the sulfur content ofbiodiesel made from lower cost, non-food feedstocks with high sulfurlevels, but again this process is cost prohibitive to produce biodieselthat is competitively priced with petroleum diesel. An embodiment of thepresent invention efficiently removes the impurities that causeunacceptable colors and/or high sulfur content of the finished biodieselproduct, thereby providing a fuel which will have unrestrictedacceptance in the market.

In addition to higher sulfur content and coloration issues, lower cost,non-food feedstocks can also contain significant quantities of highmolecular weight, low volatility unsaponifiable components which aresoluble in both the oil and the resulting biodiesel and therefore cannotbe easily removed in conventional biodiesel processes. The presence ofthese impurities may lower the perceived quality of the finishedbiodiesel product and/or impact its performance in certain operatingconditions. Further, such impurities reduce the ester content of thefinished biodiesel and thereby create potential specification issuesunder EN 14214, CAN/CGSB 3.524, and numerous customer-specificspecifications in the United States. Corn oil in particular containsmarkedly high levels of unsaponifiable components. An embodiment of theinvention disclosed efficiently removes these unsaponifiable impuritiesto produce a higher quality biodiesel with improved market acceptance.

Although the supply of corn oil is expected to increase significantly inthe near future, the characteristics described above pose significantchallenges for biodiesel producers who wish to make and market biodieselmade from it. Similar biodiesel quality and customer acceptanceobstacles also impede the current and future use of other emerging lowcost, non-food feedstocks for biodiesel production, including usedcooking oils, poultry fats, brown grease, fatty acid distillates,pennycress oil, and algal oils.

In sum, the biodiesel industry has historically used a majorityproportion of higher purity feedstocks (often edible oils and fats) andhas been restricted by fewer and less stringent product acceptancespecifications. As the industry and its customers have evolved, pricingand availability of higher purity feedstocks have pushed the industry toexplore the use of lower cost, less pure feedstocks while itsimultaneously faces tightening acceptance specifications and commercialrequirements for the finished product. Further, these lower costfeedstocks are not consistent in the nature and content of theirimpurities and exhibit great variation based not only on the underlyingsource of the oil, but on its production process and other variablesassociated with the recovery of the oils from their source materials.Conventional oil degumming pretreatment processes alone will no longerallow production of biodiesel that is universally commerciallyacceptable. As a result, what has been absent in the biodieselproduction processes are methods, systems, and compositions that allowbiodiesel producers to economically convert lower cost, non-foodfeedstocks such as corn oil, used cooking oil, poultry fats, browngrease, fatty acid distillates, pennycress oil, and algal oils intohigh-quality biodiesel that can and will conform to the variouscommercial biodiesel specifications in their current and future forms.More specifically, it is necessary to be able to produce biodiesel fromsuch feedstocks via methods and systems that overcome potentialspecification problems associated with feedstocks that contain anycombination of a variety of problem properties such as waxes,unsaponifiables, varying FFA levels, unacceptable color, and high sulfurlevels.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the technology described may be better understood byreferring to the descriptions below with the accompanying drawings. Thedrawings are not to scale and represent exemplary configurations thatdepict general principles of the technology which are not meant to limitthe scope of the invention. Dotted lines within the figures arerepresentative of different embodiments which may be included as part ofthe process.

FIG. 1 is a process flow diagram showing several embodiments of methodsfor biodiesel production.

FIG. 2 is a process flow diagram showing more specific embodiments ofthe methods for biodiesel production shown in FIG. 1.

DETAILED DESCRIPTION

The apparatus, devices, systems, products, and methods of the presentinvention will now be described in detail by reference to variousnon-limiting embodiments, including the figures which are exemplaryonly.

Unless otherwise indicated, all numbers expressing dimensions,capacities, and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”

The present invention may be practiced by implementing process steps indifferent orders than as specifically set forth herein. All referencesto a “step” may include multiple steps (or substeps) within the meaningof a step. Likewise, all references to “steps” in plural form may alsobe construed as a single process step or various combinations of steps.

The present invention may be practiced by implementing process units indifferent orders than as specifically set forth herein. All referencesto a “unit” may include multiple units (or subunits) within the meaningof a unit. Likewise, all references to “units” in plural form may alsobe construed as a single process unit or various combinations of units.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise.

As used in this specification and the appended claims, the term “fatsand oils” refers to any material of biological origin both vegetable andanimal which is a useful feedstock for making biodiesel. The feedstockmay be in a crude form containing impurities and is considered a “crudefeedstock” or “crude oil.” On the other hand, the feedstock may bepretreated using other equipment to remove impurities. The pretreatmentprocess may occur at a biodiesel production facility or at the sourcelocation or both producing a “pretreated feedstock” or “pretreated oil.”The term “refined feedstock” refers to feedstocks having sufficientlylow free fatty acid content to be used directly in transesterification.Refined feedstock may include crude alkyl esters. The term “free fattyacid” refers to aliphatic carboxylic acids having carbon chains withabout 6 to about 24 carbon atoms. Free fatty acids may be found in fatsand oils between 0 to 100 wt % and are susceptible to forming estersupon reacting with an alcohol under esterification conditions. The term“ester” is used to refer to organic esters, including mono-esters,di-esters, tri-esters, and more generally multi-esters. The term“biodiesel” is used to describe a fuel comprised of fatty acid alkylesters of long chain fatty acids derived from fats and oils. The term“alcohol” is used to refer to an organic alcohol, including monohydricalcohols, dihydric alcohols, and polyhydric alcohols generally.

The term “wax” or “waxy compounds” refers to relatively large moleculeswith at least one long saturated carbon chain that are found in oilssuch as corn oil, canola oil, sunflower oil, olive oil, poultry fat,pennycress oil, and possibly algal oils. Waxy compounds have a highmelting point (some are around 80° C.) and can cause the oil to becomecloudy when cooled. Waxes have been grouped under the category ofunsaponifiable material for the purposes of this discussion. Waxycompounds can cause biodiesel to fail certain cold soak filterabilitytests, even at concentrations less than 0.1 wt %. The term “gum” or“gums” refers to compounds (e.g., phospholipids) that may be present ina crude feedstock which tend to form insoluble precipitates whencontacted with water and emulsions in base-catalyzed transesterificationprocesses. When water is added to the crude feedstock under theappropriate conditions, gums can become hydrated (absorb water) andinsoluble so that they can be removed by a centrifugal separator.

The term “Acid Number” refers to a common measurement of the amount ofacid functional groups in the molecules in a sample. It specificallyrefers to the quantity of strong base (typically KOH) required totitrate the acid functional groups in a sample. Acid Number isconventionally expressed as milligrams of potassium hydroxide per gramof sample.

The term “sulfur” refers to the total quantity of sulfur in liquid fuelsdefined as mg/kg or parts per million (ppm). The term “unsaponifiables”refers to compounds in oils and fats that do not contain a fatty acidmoiety that can be converted to an alkyl ester molecule and thattherefore can reduce the ester content and/or yield of biodiesel. Theterm “cold soak filterability tests” refers to test methods included incommercial specifications such as ASTM D7501, CAN/CGSB 3.524 appendix A,and EN 14214 that are used to evaluate the potential cold weatherperformance of biodiesel and biodiesel blends.

The methods of the invention can accommodate a wide range of feedstocks.In some embodiments of the invention, nonexclusive examples of feedstockare fats and oils including coconut oil, palm oils, palm kernel oil,cottonseed oil, rapeseed oil, peanut oil, olive oil, linseed oil,babassu oil, tea oil, Chinese tallow oil, olive kernel oil, meadowfoamoil, chaulmoorgra oil, coriander oil, canola oil, soybean oil, corn oil,camelina oil, castor oil, pennycress oil, lard oil, jatropha oil,sunflower oil, algae oils, used cooking oils, bacon grease, choice whitegrease, yellow grease, brown grease, poultry fat, beef tallow, lard, andfish oils. Additionally, feedstocks may include purified or distilledfats and oils including fatty acid distillates, such as palm fatty aciddistillate, and others. In some cases, distillation bottoms may beconsidered a low-grade crude feedstock, including bottoms from crudebiodiesel distillation.

Corn oil is a feedstock of particular commercial significance forproducing biodiesel. Corn oil is a co-product of the grain ethanolindustry. Corn oil is typically recovered from ethanol manufacturingprocesses using a number of methods including solvent extraction,centrifugation, filter pressing, and other processes. Additional oilssuitable for biodiesel production may be recovered from other grainethanol processes including sorghum oil, wheat oil, and others,depending on the feedstock for the ethanol production process. Afterrecovery, the crude oil may be further processed as desired. In oneembodiment, crude oil recovered from a grain ethanol process is used forbiodiesel production.

One embodiment of the present invention includes a method of usinglow-cost feedstocks to produce biodiesel that meets multiple commercialproduct specifications. The invention includes one or more feedstockpretreatment, FFA refining, and biodiesel refining embodiments which maybe chosen depending on FFA content and other factors to overcomepotential specification problems associated with feedstocks havingwaxes, high free fatty acid levels, unacceptable color, highunsaponifiable levels, and high sulfur levels. Certain feedstockpretreatment, FFA refining, and biodiesel refining embodiments describedherein may be installed and used at a single biodiesel facility therebygiving the facility operator the option of choosing one process pathwayfor a particular feedstock and another process pathway for anotherfeedstock depending on feedstock characteristics or other factors. Thebiodiesel production method disclosed may include all or fewer than allof the feedstock pretreatment, FFA refining, and biodiesel refiningembodiments described herein. The particular embodiment(s) will dictatewhich feedstocks can be used to produce commercially acceptablebiodiesel. One method for crude feedstock pretreatment and biodieselrefining can produce biodiesel having physical and chemical propertiesthat conform to commercial specifications regardless of the feedstockproperties.

Crude feedstocks (105) containing various impurities requirepretreatment and/or FFA refining before being subjected to atransesterification process to convert the refined feedstock to crudebiodiesel (150) and finally a biodiesel purification process to makehigh quality purified biodiesel (160) that meets multiple commercialspecifications. An exemplary method (100) with reference to FIG. 1 isoutlined for processing crude feedstock (105) into glycerin (145) andpurified biodiesel (160) meeting commercial product specifications. Thecrude feedstock (105) arrives at the biodiesel production facility andis discharged into crude feedstock storage. Compatible feedstocks may becombined and stored in a shared tank before being processed. Crudefeedstock (105) first undergoes a feedstock pretreatment process (110)that depends on its FFA content and other properties to produce apretreated feedstock (115).

The pretreated feedstock (115) may then be subjected to an FFA refiningprocess (120) which removes and/or converts FFA by way of: FFA stripping(dashed line 2) or esterification/glycerolysis (dashed line 3) to yielda refined feedstock (125). Optionally, FFA refining (120) may yield astream of crude biodiesel (150) in the case of FFA stripping followed byesterification of the fatty acid distillate. As another option, FFArefining (120) may yield a stream of glycerides or refined feedstock(125) in the case of FFA stripping followed by glycerolysis of the fattyacid distillate. In one embodiment, as shown by dashed line 1,pretreated feedstock (115) having sufficiently low levels of FFA to becategorized as refined feedstock (i.e., the crude feedstock waschemically refined to remove FFA in feedstock pretreatment (110) or wasrefined elsewhere) bypasses the FFA refining unit (120). Refinedfeedstock (125) is processed in a transesterification process (130) toyield crude biodiesel (150) and crude glycerin (135). Crude glycerin(135) is refined in a glycerin refining unit (140) yielding glycerin(145) which may be recycled into the FFA refining process (120) forglycerolysis. Crude biodiesel (150) undergoes a final biodiesel refiningprocess (155) to produce a commercially-acceptable purified biodieselproduct (160). Wet alcohol from biodiesel refining (155) and glycerinrefining (140) is sent to an alcohol recovery unit (165) to separatewater (175) and recover dry alcohol (170). Embodiments of the unitoperations of FIG. 1 are described in more detail in FIG. 2.

FIG. 2 shows process embodiments similar to the embodiments shown inFIG. 1, except FIG. 2 shows additional embodiments and process steps inmore detail. Crude feedstock (105) is received into storage at thebiodiesel production facility. Compatible feedstocks may be combined andstored in a shared tank before they are processed further. Crudefeedstocks (105) are pretreated and refined as dictated by their FFAcontent and other feedstock properties. Crude feedstock (105) mayundergo either a chemical refining (205) (dashed line A), degumming(210) (dashed line B), or a bleaching and polishing (230) (dashed lineC) pretreatment step depending on its physical and chemicalcharacteristics. Typically chemical refining (205) (dashed line A) isperformed for crude feedstocks having a relatively low amount of FFA(<4%, for example). In one embodiment, an acid, such as phosphoric acid,may be added to the crude feedstock (105) in the chemical refining unit(205) with or without additional water. In such a process, the acid andwater perform a similar function as in the degumming unit (210).Regardless of acid use, a strong base (215), such as NaOH (caustic soda)or KOH (potash), is added to the crude feedstock from unit (105) toreduce the free fatty acid content to a desired level (<0.2%, forexample) by converting the FFAs to soaps and also to neutralize anyadded acid. In one embodiment, soapstock is composed of water, soaps,hydrated gums if present, and any other hydratable, polar, or solidcomponents in the crude feedstock. This soapstock (225) is then removedin a centrifugal separator (220).

Alternatively, feedstocks having greater than about 4 wt % FFA aretypically pretreated with a degumming step (210) (dashed line B),although in particular situations feedstocks with lower amounts of FFAmay also be pretreated with degumming (210). An acid, such as phosphoricacid, may be added to the crude feedstock (105) in the degumming unit(210) which may be heated, for example, using steam (water). In such aprocess, the acid and water hydrate naturally-occurring gums in the oilor fat so that they can be separated from the crude feedstock. Thedegumming unit (210) is also capable of facilitating the removal ofother hydratable and/or polar impurities in the crude feedstock as wellas solids. Optionally, a base (215), such as sodium hydroxide (causticsoda), may be added to the degumming unit (210) in order to neutralizethe acid used for degumming. Excess base may also be added to neutralizea minority portion of the free fatty acids.

In both embodiments described above, feedstock leaving the chemicalrefining unit (205) or the degumming unit (210) is processed in acentrifugal separator (220). The centrifugal separator unit (220)removes the aqueous phase and any hydratable or polar compounds from thecrude feedstock formed in unit (205) or (210) in addition to any solids.This aqueous phase may be referred to as soapstock (225) in bothembodiments.

Once the crude feedstock (105) has passed through the centrifugalseparator (220) it may undergo one or more drying, bleaching andpolishing steps in unit (230) including heat bleaching or clay bleachingsteps to reduce color, solids, residual soaps, moisture and otherimpurities in the partially refined feedstock. With deeply coloredfeedstocks, the bleaching and polishing steps (230) do not typicallyremove enough color to eliminate the potential for commercial rejectionof the resulting biodiesel. In the case where corn oil is the crudefeedstock, bleaching and polishing steps (230) do not typically removeenough of the characteristic deep red color to prevent the resultingbiodiesel from resembling fuel that has been dyed for off-road use only.In one embodiment the feedstock is bleached and dried in the same unitoperation. In another embodiment the feedstock is dried by avacuum-dryer, flash drum, or other such means to a desired water contenteither before and/or after it enters the bleaching unit. The desiredwater content depends on the type of filter material that is used in thebleaching unit and the impurities that are present in the feedstock atthis point.

After the feedstock has been dried and bleached it enters a polishingfilter where any remaining filterable impurities are removed, along withany fine particles of filter material from the bleaching step. Forfeedstocks containing waxy compounds, the preceding steps may removesome wax if operated at low temperatures (<150° F., for example), butsince wax is somewhat soluble even at relatively low temperatures someof the waxes are retained in the feedstock and are carried through tothe biodiesel. Also, the viscosity of oils and fats increasesdramatically at lower temperature, which means lower refiningtemperatures can dramatically reduce the feasible throughput of anyprocess unit that has to operate at a lower temperature.

In one embodiment, where corn oil, used cooking oil, fatty aciddistillate, or other feedstocks are pretreated, the feedstock (105) maynot necessarily require chemical refining (205), degumming (210), orcentrifugation in unit (220) and may instead pass directly (dashed lineC) to the bleaching and polishing unit (230) to yield a dry pretreatedfeedstock (115). In fact, some feedstocks may form an irresolvableemulsion in the centrifuge (220) if they are subjected to a degumming(210) and/or washing step prior to the centrifuge (220). Therefore, inone embodiment, feedstocks (105) that emulsify are not subjected tounits (205) or (210) and (220) and may instead be fed directly (dashedline C) to the bleaching and polishing unit (230) after bypassing thedegumming/chemical refining and centrifugal separation processes toyield a pretreated feedstock (115). Furthermore, some crude feedstocks(105) such as certain fatty acid distillates may not require feedstockpretreatment (110) at all and may therefore pass directly to FFAconversion unit (250) (dashed line 3) as a pretreated feedstock (115).

Depending on the effectiveness of the initial crude feedstockpretreatment strategy and the pretreated feedstock FFA content, thepretreated feedstock (115) may optionally undergo further processing. Iffree fatty acids have been removed in the chemical refining unit (205)and centrifuge (220) in the form of soapstock (225), the pretreatedfeedstock (115) may continue directly to the transesterification processas a refined feedstock (125) as shown by dashed line 1. However, if asignificant quantity of free fatty acids remain (>0.2%, for example)because the crude feedstock (105) was pretreated with a degummingprocess (210) (dashed line B) and/or a bleaching and polishing step(230) (dashed line C), the pretreated feedstock (115) requires furtherprocessing in either the FFA stripping unit (235) or in the FFAconversion unit (250). Free fatty acids in the crude feedstock (105) aregenerally undesirable in the transesterification process (130) becausethey form soaps in the oil when they react with the base catalyst usedto drive the transesterification reaction. Therefore, they must beeither removed or converted or both. There are two primary processingoptions to reduce FFA levels in the pretreated feedstock (115): 1)stripping or deacidification to physically remove FFAs from thefeedstock (235) and 2) chemical conversion by esterification orglycerolysis (250). Glycerolysis is a subcategory of esterification inwhich glycerol, an alcohol, is used to convert FFAs into glycerides,which are fatty acid esters of glycerol. An advantage of this inventionover prior art is that a feedstock with any FFA content (0-100 wt %) canbe processed with the appropriate feedstock pretreatment embodiment(110).

In one embodiment shown by dashed line 2, the pretreated feedstock (115)is stripped of free fatty acids along with other components of lowmolecular weight relative to glycerides in a physical FFA refining stepusing distillation (235). Although the FFA stripping step can beperformed on feedstocks having any FFA level, a preferred FFA level isbetween about 0.2 wt % FFA and about 30 wt % FFA. The FFA stripping step(235) may employ steam, hot oil, or other thermal fluid to heat thecrude feedstock. The distillation may occur under vacuum to remove freefatty acids from the oil phase by evaporation in unit (235). The FFAstripping step (235) may employ a distillation column, wiped-filmevaporator, or other such equipment and it may optionally include theinjection of steam into the distillation unit to facilitate theseparation of the FFAs from the remainder of the feedstock. Two productstreams can be produced from FFA stripping (235): a relatively purefatty acid distillate (240) made up of greater than about 50 wt % FFAand the stripped feedstock (245) containing less than about 0.5 wt %FFA. The stripped feedstock stream (245) is sufficiently purified duringFFA stripping (235) that it can enter the transesterification process asa refined feedstock (125). The fatty acid distillate stream (240) may besold as a final product or may undergo further processing to chemicallyconvert the FFAs in unit (250) (dashed line 4).

FFA stripping can have additional benefits beyond FFA reduction. As oneexample, corn oil subjected to FFA stripping in unit (235) issubstantially less red than crude or esterified corn oil. That is,compounds are modified or removed along with the FFA such that biodieselmade from stripped corn oil does not resemble dyed diesel fuel.

In another embodiment, pretreated feedstock (115) is directly processedin unit (250). Feedstocks having between 0.1-100 wt % FFA can beprocessed in the FFA conversion unit (250) to convert FFA into esters byway of esterification or glycerides by way of glycerolysis (dashed line3). Fatty acid distillate (240) from FFA stripping (235) may also beprocessed in the FFA conversion unit (250) (dashed line 4).

In one embodiment pretreated feedstock (115) (following dashed arrow 3)and/or fatty acid distillate (240) (following dashed arrow 4) isesterified to form alkyl esters in unit (250). In this embodiment freefatty acids may be esterified using a homogeneous and/or heterogeneouscatalyst with an alcohol (e.g. dry alcohol from unit 170) to form fattyacid alkyl esters. The homogeneous catalyst may include sulfuric acid,methanesulfonic acid, p-toluene sulfonic acid, hydrochloric acid, orother suitable acid. The heterogeneous catalyst may include an acid ionexchange resin such as Amberlyst BD20 sulfonic acid ion exchange resinfrom Rohm and Haas and Lewatit® catalyst from Lanxess, other solidcatalysts such as metal oxide materials, or enzymatic catalysts.Esterification of FFAs in the FFA conversion unit (250) may take placein one or more reactors and the product may be separated, washed and/orrecycled back into itself until the FFA is low enough to leave as arefined feedstock (125) or blended into the refined feedstock (125).Homogeneous acid catalyst may or may not be removed and/or neutralizedbefore leaving the FFA conversion unit (250). In one embodiment FFA inthe product stream contains less than about 5 wt %, 4 wt %, 3 wt %, 2 wt%, 1 wt %, 0.5 wt %, 0.3 wt % or 0.1 wt % FFA before enteringtransesterification as either part or all of the refined feedstock(125). Alternatively, if fatty acid distillate (240) converted in theFFA conversion unit (250) has sufficiently high alkyl ester content orif the alkyl esters are phase separated from the product mixture thealkyl ester-rich stream may bypass transesterification (130) entirelyand proceed directly to biodiesel refining (155) as crude biodiesel(150).

In the case where corn oil is the feedstock subjected to free fatty acidesterification in unit (250), the red color of the corn oil may in factbecome deeper than the initial crude corn oil. Thus, the resulting cornoil biodiesel may more strongly resemble dyed petroleum diesel fuelunless it is further processed to remove the color. Similarly, the browncolor of other crude feedstocks may deepen during FFA conversion in unit(250) and thus require additional processing downstream to reduce thecolor of the biodiesel to commercially acceptable levels. Generallyspeaking, discouraging color issues may be either improved orexacerbated during feedstock pretreatment (110) and FFA refining (120)but they are often exacerbated.

In another embodiment, pretreated feedstock (115) (following dashedarrow 3) and/or fatty acid distillate (240) (following dashed arrow 4)undergo glycerolysis to form glycerides in unit (250). In thisembodiment, free fatty acids from the pretreated feedstock (115) orfatty acid distillate (240) may be reacted with glycerin from unit (145)in FFA conversion unit (250) to form mono-, di-, and triglycerides,which can then be transesterified to produce biodiesel. Various processequipment may be used within the FFA conversion unit (250) to accomplishthis step and reduce the FFA of the products stream to less than about 5wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt %, 0.5 wt %, 0.3 wt % or 0.1 wt % FFAbefore entering transesterification as a refined feedstock (125).

Thus, feedstock (105) containing any quantity of FFA can be processed byat least one of the pretreatment (110) and FFA refining (120) methodsdescribed above whereby FFAs are removed in a chemical refining unit(205), a physical refining unit (235) and/or converted by esterificationor glycerolysis in a FFA conversion unit (250). However, in eachpretreatment (110) and FFA refining (120) approach a small amount offree fatty acids typically remains and ends up in the finished biodieselproduct, which increases the biodiesel Acid Number. Because certainfeedstocks can contain impurities that contribute to biodiesel AcidNumber when assessed according to ASTM D664 Method B, furtherpurification must be performed on biodiesel made from such feedstocks inorder to meet commercial specifications and obtain full marketacceptance. This is particularly true for biodiesel produced fromfeedstocks such as corn oil and some fatty acid distillates. When cornoil, corn oil biodiesel and fatty acid distillates (along with biodieselproduced therefrom) are analyzed for Acid Number with ASTM D664 MethodB, they can exhibit a second titration inflection point caused bycompounds that are titrated after the free fatty acids. Therefore thefeedstock tends to have an Acid Number greater than the amount of FFA inthe oil, and this Acid Number increase is imparted to the resultingbiodiesel without additional downstream processing.

Once the feedstock has been pretreated (110) and refined (120) it entersthe transesterification process (130) and then on to the biodieselrefining process (155). There are several processes that may be used toproduce biodiesel from oils and fats, including base-catalyzedtransesterification, acid-catalyzed transesterification and enzymatictransesterification.

In one embodiment, biodiesel is produced from feedstock usingbase-catalyzed transesterification in one, two, three, or more reactors.In one embodiment, refined feedstock (125) is subjected to atransesterification reaction process and then refined to producepurified biodiesel (160) and glycerin (145). This transesterificationreaction is based on the chemical reaction of the mono-, di-, andtriglycerides contained in the feedstock with an alcohol in the presenceof a base catalyst. The base catalyst used in the transesterificationreaction may be selected from several different basic materials.Suitable catalysts include, for example, NaOH or caustic soda, KOH orpotash, CH₃NaO (sodium methoxide), and CH₃KO (potassium methoxide). Thealcohol used in the transesterification reaction may be selected from,for example, methanol or ethanol.

As the transesterification reaction is carried out in a first reactor(255), dry alcohol (170) and catalyst or enzymes (260) may be deliveredto the refined feedstock (125) in parallel, as separate reactioncomponents, or the alcohol and catalyst can be delivered to the refinedfeedstock (125) as a mixture. When delivered as a mixture, the catalystmay be dissolved or dispersed in the alcohol by any suitable means priorto charging the mixture into the feedstock. Alternatively, the catalystmay be provided as a liquid and mixed with the alcohol, limiting theneed for dissolution of the catalyst in the alcohol prior to mixing thealcohol and catalyst with the feedstock. Where the catalyst is mixedwith the alcohol as a liquid, the catalyst may be added to the alcoholby, for example, one or more metering pumps. In addition, because analkaline catalyst might be sensitive to water, the catalyst may bestored in a tank protected with a nitrogen layer. In carrying out thetransesterification reaction, the dry alcohol (170), catalyst or enzymes(260), and refined feedstock (125) may be charged directly into thefirst reactor (255) or may be mixed before entering the reactor (255).

The reaction system can be closed to the atmosphere to prevent loss ofthe alcohol used in the transesterification reactor unit (255). As thereaction components are mixed, the mixture may be kept just below theboiling point of the alcohol to speed the reaction time by maximizingreaction temperature while minimizing the amount of alcohol lost duringreaction. Alternatively, the reaction mixture may be heated above theboiling point of the alcohol in a vessel that is either pressurized oruses reflux to maintain the alcohol largely in a liquid state. Allvessels which contain alcohol, may also be connected to a vent system tocapture any alcohol vapors. Captured alcohol vapors may be fed into acondensing system that recovers the alcohol and recycles the alcoholback into the refining process. An excess amount of alcohol is typicallyused to ensure total conversion of the feedstock glycerides into thedesired ester product.

The transesterification reaction mixture leaves the reactor (255) andenters a phase separation unit (265). In the phase separation unit (265)the reaction mixture is separated into two-phases: an ester-rich phase(crude biodiesel) that is transferred to an additional reactor orreactors (270) and a glycerin-rich phase (crude glycerin) collected inunit (135). The crude glycerin (135) is more dense than the crudebiodiesel (150) and the two phases can be separated by gravityseparation in a decanting vessel or, if needed or desired, bycentrifugal separation.

In one embodiment, transesterification of the feedstock takes place inone or more mixing-settling process units. In such process units, thetransesterification reaction occurs in a mixer or reactor and the crudebiodiesel and crude glycerin resulting from the transesterificationreaction form two distinct phases that can be separated by a settlingprocess. If two or more mixing-settling process units are used, thefeedstock and the intermediate product, respectively, may flowsuccessively through the two or more mixing-settling processes. Eachmixing-settling process can be supplied with the desired amount ofalcohol and catalyst. The reactors included in the mixing-settlingprocess units can be multi-stage in design, comprising various reactionchambers or zones in order to achieve maximum conversion efficiency tothe ester product. The settling steps allow phase separation to approachthe limit of solubility, which facilitates downstream purification ofthe biodiesel and glycerin products.

Once the transesterification reaction is complete in the second reactor(270), the reaction mixture enters a second phase separation unit (275).In one embodiment, acid (280) is mixed with the reaction mixture leavingreactor (270) to deactivate the transesterification catalyst beforeentering the phase separation unit (275). In other embodiments thecatalyst is deactivated after the phase separation unit. The acid can bediluted with water (175) prior to being introduced to the reactionmixture in an acid dilution vessel (285). In the phase separation unit(275) the reaction mixture is again separated into two-phases: anester-rich phase or crude biodiesel (150) and a glycerin-rich phase orcrude glycerin (135) sent to unit (290). Each of these crude phases mayinclude a significant amount of the excess alcohol used in the reaction.Moreover, the crude reaction products may include other impurities suchas excess catalyst, soaps, salts, water, and high boiling impurities. Inone embodiment, some or all of these impurities may be treated orremoved from the crude reaction products before the biodiesel and theglycerin phases are separated in unit (275).

In one embodiment, after the crude biodiesel (150) and crude glycerin(135) have been separated in unit (275), crude glycerin (135) may betreated with a suitable acid from an acid dilution vessel (285) toneutralize the residual catalyst, and crude biodiesel (150) can besubjected to a water wash in unit (295) to remove glycerin, salts, andsoaps. The separated crude glycerin (135) may be subjected to additionalpurification in an evaporation step to remove any remaining alcohol. Onesuch distillation and drying step is performed in unit (290). Theglycerin alcohol stripper (290) removes alcohol and water which iscollected in a wet alcohol unit (315) leaving a glycerin product whichis approximately 78-98% pure glycerin. This glycerin (145) can befurther refined to a purity of about 99% or higher using additionalprocessing techniques, such that the glycerin product is suitable foruse in high purity applications such as cosmetics or pharmaceuticals.

Crude biodiesel (150) leaving the phase separation unit (275) will stillinclude impurities and therefore must be purified in one or more unitoperations. The order and number of these operations may vary dependingon crude feedstock properties, pretreatment process, transesterificationprocess, and economic feasibility. After the crude biodiesel (150) isseparated from crude glycerin (135) in unit (275), it is typicallysubjected to further biodiesel refining (155). For example, afterseparation, the crude biodiesel may contain residual alcohol, glycerin,small amounts of catalyst, salts, and soaps. This may be the case evenif the crude reaction products are refined to remove or neutralizeimpurities prior to separation. In one embodiment, crude biodiesel (150)is subjected to a flash evaporation or distillation processes to removeexcess alcohol immediately after the phase separation unit (275) beforethe water wash unit (295). In another embodiment, crude alkyl esters(dotted arrow from the FFA conversion unit (250)) may bypasstransesterification and directly enter the water wash (295) as a crudebiodiesel (150) or another step in the biodiesel refining process (155).In one embodiment, crude biodiesel (150) from FFA conversion unit (250)is distilled in biodiesel refining unit (155) to produce a purifiedbiodiesel (160) and distillation bottoms (180) which may be recycled asa crude feedstock (105) for biodiesel, used as a feedstock for otherrenewable fuels, or directly used as a renewable fuel product.

In one embodiment of biodiesel refining (155), crude biodiesel (150) isfirst washed in unit (295) in order to remove water-soluble substancessuch as soaps and residual catalyst. Soaps that may be present in thewater wash unit (295) may be split to avoid the formation of emulsionsduring washing, for example, by the addition of an acid. Dilutedhydrochloric acid, such as a 3.7% solution, is suitable for such anapplication and can be prepared and added as necessary. In oneembodiment, the biodiesel wash process may simply include gentle mixingof the crude biodiesel (150) with water (175) in unit (295), whichremoves residual water soluble and polar impurities as they are taken upin the aqueous phase.

If the crude biodiesel (150) is processed through such a washing step inunit (295), the washed biodiesel may contain excess water. Such excesswater may be removed, for example, in a phase separation unit (300).Water from the phase separation unit (300) may be recycled back to theacid dilution unit (285) for reuse. In one embodiment, the crudebiodiesel (150) may be stripped of alcohol and water in the biodieselalcohol stripper (305), which may consist of distillation vessels,distillation columns, short path distillation, wiped film evaporators,thin film evaporators, falling film evaporators, and other strategies.Water (175) is removed from wet alcohol (315) in the alcoholrectification unit (320). The water (175) can be recycled into the waterwash unit (295) and the dry alcohol (170) is recycled back to thetransesterification reactor(s) (255) and (270).

While some dried biodiesel (158) (output of the biodiesel alcoholstripper (305)) products made from certain edible-quality feedstockssuch as canola oil, lard, and technical tallow may be ready for use,distribution, or sale after leaving the biodiesel alcohol stripper(305), dried biodiesel products made from low-cost feedstocks will nottypically meet commercial biodiesel specifications even when theappropriate feedstock pretreatment (110) and FFA refining (120) optionsare employed. Particularly, dried biodiesel (158) made from emergingnon-food feedstocks such as corn oil, used cooking oil, poultry fat,pennycress oil, fatty acid distillates, or algae oil may requireadditional processing after the biodiesel alcohol stripper (305) beforeit is ready for use, distribution, or sale. However, the combination ofan appropriate biodiesel refining process (155) with an appropriatefeedstock pretreatment (110) and FFA refining (120) process will providea purified biodiesel (160) that meets commercial specificationsregardless of the initial feedstock properties.

Depending on the feedstock and its impurities, the biodieselpurification unit (310) may differ. In one embodiment, the driedbiodiesel (158) is subjected to a cold filtration process in unit (310)such that high melting components, such as proteins, waxes, and certainunsaponifiables, are cooled to below their solubility point and removedby filtration. In this way, the dried biodiesel (158) can be made tomeet commercial cold soak filterability tests. Generally, combining thecold filtration option with feedstock pretreatment (110) and FFArefining (120) has many advantages. However, certain feedstocks maycause the filter(s) to plug more quickly and require more frequent downtime for filter changes and higher operating costs. Such feedstocksinclude those with high wax content, such as corn oil, sunflower oil,olive oil, pennycress oil, certain poultry fats, and possibly algaloils. Because of their solubility in alkyl esters across a widetemperature range, waxes cannot always be fully removed in acost-effective manner using a combination of a pretreatment (110) andFFA refining (120) process and a cold filtration process or similarwinterization technique. Cold filtration techniques may use diatomaceousearth (DE) or other filter media to increase the effectiveness of thefiltration.

In another embodiment, the dried biodiesel (158) is subjected to amembrane filtration process in unit (310) such that high meltingcomponents, such as proteins, waxes, and certain unsaponifiables, arecondensed and removed below their melting point. Membrane filtration mayoccur at cold temperatures such that condensed particles are more easilyfiltered or at higher temperatures using membranes with very small poresthat can separate larger or more polar molecules from a solution (e.g.,nanofiltration). In this way, the dried biodiesel (158) can be made tomeet commercial biodiesel specifications. Membrane filtration techniquesmay include ceramic membranes, polymer membranes, molecular sieves, andcarbon fibers or nanotubes. In one embodiment, product leaving the phaseseparation unit (300) may directly enter a membrane filtration unitwhich removes both methanol and water rather than passing through abiodiesel alcohol stripper (305).

In another embodiment, the dried biodiesel (158) is subjected to a resinfiltration process in unit (310) such that impurities, including water,are removed. In this way, the dried biodiesel (158) can be made to meetcommercial biodiesel specifications. Resin filtration techniques mayinclude dry wash resins, ion-exchange resins and other absorbent resins.In one embodiment, product leaving the phase separation unit (275) or(300) may directly enter a resin filtration unit which may removemethanol, glycerin, water and other impurities rather than passingthrough additional purification units.

In another embodiment, dried biodiesel (158) from the biodiesel alcoholstripper (305) can be subjected to distillation in unit (310) to removeor reduce the levels of waxes, unsaponifiables, soaps, color compounds,sulfur compounds, high-boiling compounds with acid or base functionalgroups, and mono-, di-, and triglycerides. Such a distillation processcan be performed by various process equipment, including distillationvessels, distillation columns, short path distillation, wiped filmevaporators, thin film evaporators, falling film evaporators, and otherstrategies. The resulting biodiesel is purified (160) and should becommercially acceptable in spite of the problematic components that werepresent in the initial crude feedstock.

In one embodiment, biodiesel purification unit (310) is a short pathdistillation process (e.g., a wiped film evaporator) used to reducelevels of sulfur compounds, waxes, soaps, phospholipids, colorimpurities, high molecular weight compounds such as polymerized fattyacid compounds and compounds with acid functional groups, glycerides(mono-, di- and triglycerides), and unsaponifiable material comprisingat least one of sterols, sterol derivatives, proteins, and pigments.

In another embodiment, biodiesel purification unit (310) may be adistillation column when, in addition to the impurities discussed in thepreceding paragraph, a particularly low level of monoglycerides iscritical for commercial acceptance, such as less than about 0.2 wt %.

In one embodiment, biodiesel distillation in unit (310) purifies thecrude biodiesel to reduce protein, wax, and unsaponifiables content suchthat the purified biodiesel product will pass cold soak filterabilitytests. In one embodiment biodiesel distillation purifies the crudebiodiesel to remove compounds causing a second inflection point andelevated Acid Number when titrated according to ASTM D664 Method B. Inone embodiment biodiesel distillation purifies the crude biodiesel toremove other acidic compounds such that the purified biodiesel productwill have a reduced Acid Number. In one embodiment, the purifiedbiodiesel product (160) has an Acid Number of less than about 1, 0.5,0.3 or 0.1. In one embodiment biodiesel distillation purifies the crudebiodiesel to remove unsaponifiables such that the purified biodieselproduct will have increased ester content. In one embodiment biodieseldistillation purifies the crude biodiesel to reduce color compounds suchthat the purified biodiesel product will have a lighter color than theoriginal feedstock. In one embodiment biodiesel distillation purifiesthe crude biodiesel to reduce color compounds such that the purifiedbiodiesel product will meet color requirements for customer acceptanceand/or will not appear similar to diesel dyed for off-road use. In oneembodiment biodiesel distillation purifies the crude biodiesel to removeglycerides such that the purified biodiesel product will meet commercialmonoglyceride specifications such as the new monoglyceride specificationin ASTM D6751 and future glyceride specifications should they beintroduced.

In one embodiment, biodiesel distillation occurs between 200-300° C. and800-0 Torr. In another embodiment, biodiesel distillation occurs between230-290° C. and 40-0 Torr. In yet another, biodiesel distillation occursbetween 240-280° C. and 5-0.01 Torr.

In one embodiment, the biodiesel product produced from the biodieselpurification process will have a wax content of less than 0.1 wt %, anunsaponifiables content of 2 wt % or less, a soap content of 50 ppm orless, a sulfur content of 500 ppm or less, a monoglyceride content lessthan 0.6 wt %, a cold soak filtration result of 360 seconds or less anda lighter color than the original feedstock.

In another embodiment, the biodiesel product produced from the biodieselpurification process will have a wax content of less than 0.05 wt %, anunsaponifiables content of 1 wt % or less, a soap content of 20 ppm orless, a sulfur content of 15 ppm or less, a monoglyceride content lessthan 0.5 wt %, a cold soak filtration result of 240 seconds or less anda lighter color than the original feedstock.

In one embodiment, the biodiesel product produced from the biodieselpurification process will have a wax content of less than 0.01 wt %, anunsaponifiables content of 0.5 wt % or less, a soap content of 10 ppm orless, a sulfur content of 10 ppm or less, a monoglyceride content lessthan 0.4 wt %, a cold soak filtration result of 200 seconds or less anda lighter color than the original feedstock.

The invention is illustrated in detail below with reference to theexamples, but without restricting it to them.

EXAMPLES Example 1 Feedstock Properties and Corresponding ProcessingOptions

Feedstock properties determine how the feedstock should be processed inorder to produce a commercially acceptable biodiesel. However, there areusually multiple processing options available and the chosen pathway isconstrained by a combination of what is economically feasible andend-product quality. Depending on the feedstock more than one acceptablefeedstock pretreatment (110), free fatty acid refining (120) andbiodiesel refining (155) processing pathways may exist. Table 1 outlinesa number of feedstock refining pathways that correspond to the ProcessUnits depicted in FIG. 2, though other options may exist.

TABLE 1 Feedstock Refining Pathways Feedstock Refining -110, 120 Op-FIG. 2 tion Pretreatment -110 FFA Refining -120 Process Units A1Chemical Refining + Bypass (1) 205, 230 Bleaching (A) B1 Degumming +Bleaching Bypass (1) 210, 230 (B) B2 Degumming + Bleaching FFA Stripping(2) 210, 230, 235 (B) B3 Degumming + Bleaching FFA Conversion (3) 210,230, 250 (B) B4 Degumming + Bleaching FFA Stripping + 210, 230, 235, (B)FFA Conversion (4) 250 C2 Bleaching (C) FFA Stripping (2) 230, 235 C3Bleaching (C) FFA Conversion (3) 230, 250 C4 Bleaching (C) FFAStripping + 230, 235, 250 FFA Conversion (4)

Table 2 outlines biodiesel refining pathways that correspond tobiodiesel purification unit (310) in FIG. 2. It should be noted that thefiltration option may include any number of filtration techniques,including cold filtration, membrane filtration, the use ofchemically-active adsorbents or resins (i.e., “dry washing”), or othersuch methods. Similarly the distillation option may include any numberof distillation techniques, including atmospheric distillation, vacuumdistillation, or other such methods.

TABLE 2 Biodiesel Refining Pathways Biodiesel Refining -155 OptionBiodiesel Purification -310 F Filtration D Distillation

Table 3 provides a list of feedstocks, feedstock properties, andcorresponding processing pathways with respect to the feedstock refiningand biodiesel refining pathways listed in Table 1 and Table 2,respectively. The processing pathways in Table 3 are examples of howparticular feedstocks could be processed to produce commerciallyacceptable biodiesel, however, other acceptable pathways may exist. Eachfeedstock requires an appropriate combination of feedstock refiningpathway and biodiesel refining pathway in order to produce commerciallyacceptable biodiesel.

TABLE 3 Example Feedstock Properties and Processing Pathways ExampleFeedstock properties Crude Feedstock FFA Wax Unsaponi- ProcessingPathway Examples Content Content Color Sulfur fiables Options Corn OilHigh High High Low High C2 + D, C3 + D, C4 + D Poultry Fat High HighHigh High Low B2 + D, B3 + D, B4 + D Crude Soybean/Canola Oil Low LowLow Low Low A1 + F, B1 + F Used Cooking Oil High Low High Low Low B2 +D, B3 + D, B4 + D, C2 + D, C3 + D, C4 + D Pennycress/Algae/OtherHigh/Low High/Low High Low High/Low A1 + D, B1 + D, B2 + D, B3 + D, B4 +D Fatty Acid Distillate High Low High High Low C3 + F, C3 + D

Example 2 Acid Esterified Corn Oil Biodiesel with and withoutDistillation Purification

Corn oil from a grain ethanol process was converted into commerciallyacceptable biodiesel using an acid esterification FFA refining processcoupled with cold filtration and distillation biodiesel refining steps.Two samples of corn oil biodiesel were obtained: one immediately aftercold filtration using diatomaceous earth (DE) and a second after bothcold filtration and distillation to compare the effects. The crude cornoil feedstock was acid esterified with methanol using homogeneoussulfuric acid (H₂SO₄) catalyst to convert free fatty acids to methylesters. The strong acid used during esterification was neutralized withsodium hydroxide (NaOH) before a water wash. Once the feedstock wasdried it was sent to a base-catalyzed transesterification process. Afterbeing separated from the glycerin and removing the methanol and water,the dried biodiesel was subjected to purification by cold filtration ordistillation in a wiped-film evaporator. The physical and chemicalproperties of the dried biodiesel before and after distillation areprovided in Table 4 below. Cold filtration of the dried biodiesel usingDE produces biodiesel with acceptable Cold Soak Filtration Time, AcidNumber, Sulfur, and Monoglycerides according to ASTM D6751. However,distillation of the cold filtered, dried biodiesel clearly reduces thewax content (as indicated by Turbidity), Acid Number (and number ofinflection points), and Gardner Color (a yellow-to-red color scale)which are particularly problematic properties for corn oil biodiesel.Therefore, a combination of esterification of free fatty acids (FFA) andbiodiesel distillation can be used to produce purified corn oilbiodiesel that meets more stringent commercial biodiesel specificationsthan a combination of FFA esterification and cold filtration.

TABLE 4 Properties of Acid Esterified Corn Oil Biodiesel with ColdFiltration and Distillation Esterified Corn Oil Biodiesel Cold ColdFiltered & Properties Filtered Distilled Wax Reduction (IndirectMethods): Cold Soak Filtration Time [ASTM D7501] (s) 96 — Turbidity(Nephelometric Turbidity Unit or NTU) 22.3 1.4 Acid Number per ASTM D664Method B 0.453 0.298 (mg KOH/g) Number of Inflection points 2 1 Nitrogen(ppm) 14.5 4.8 Sulfur (ppm) 6.0 3.0 Monoglycerides (wt %) 0.49 0.53Diglycerides (wt %) 0.06 <0.005 Triglycerides (wt %) <0.005 <0.005Color: Gardner Color (ASTM D1544) 15 9 Resemblance to Dyed Diesel yes no

Example 3 FFA Stripped Corn Oil Biodiesel with and without DistillationPurification Compared to Filtration

Corn oil from a grain ethanol process was converted into biodiesel usingan FFA stripping process for FFA refining followed bytransesterification of the stripped feedstock and two purificationtechniques: room temperature filtration using a single-layer paperfilter and distillation. A sample of dried corn oil biodiesel wasobtained before and after the biodiesel refining units to compare theeffectiveness of each method in conjunction with the FFA refiningapproach. The crude corn oil feedstock was stripped of FFA beforeentering a base-catalyzed transesterification process. After beingseparated from the glycerin and removing the methanol and water, thedried biodiesel was subjected to purification by either a filtrationstep or distillation in a wiped-film evaporator. The physical andchemical properties of the biodiesel before and after purification byfiltration or distillation are provided in Table 5 below. The filtrationand distillation processes both improve the biodiesel quality comparedto unpurified dried biodiesel. However, the effect of distillation ismore pronounced than filtration especially in terms of relative waxreduction (as indicated by the Cold Soak Filtration time and Turbidity),Acid Number, unsaponifiables, nitrogen, sulfur, di- and triglycerides,and color. Although distillation was able to reduce the number ofinflection points and overall Acid Number, the high initial Acid Numberof the unpurified dried corn oil biodiesel used in this trial indicatesthe importance of having both FFA refining and biodiesel refining. Inthis laboratory example, the FFA refining process was not optimized andwas therefore not able to sufficiently remove sufficient FFAs to producebiodiesel that meet the ASTM D6751 specification for Acid Number.

TABLE 5 Properties of Stripped Corn Oil Biodiesel with Filtration orDistillation Stripped Corn Oil Biodiesel Properties Unpurified FilteredDistilled Wax Reduction (Indirect Methods): Cold Soak Filtration Time720^(a)   720^(b)   176 [ASTM D7501] (s) Turbidity (NephelometricTurbidity 84.0  29.0  1.3 Unit or NTU) Acid Number per ASTM D664  1.021 0.955 0.908 Method B (mg KOH/g) Number of Inflection points 2   2   1Unsaponifiables (wt %)  0.77%  0.97% 0.27% Nitrogen (ppm) 23.1  21.5 6.7 Sulfur (ppm) 6.7  6.5  3.7 Monoglycerides (wt %) 0.62 0.61 0.64Diglycerides (wt %) 0.09 0.10 <0.005 Triglycerides (wt %) 0.04 0.04<0.005 Color: Gardner Color (ASTM D1544) 11    11    5 Resemblance toDyed Diesel yes yes no ^(a)150 mL out of 300 mL remaining after 720 s^(b)120 mL out of 300 mL remaining after 720 s

Example 4 FFA Stripped Used Cooking Oil Biodiesel with and withoutDistillation Purification Compared to Cold Filtration

A mixture of used cooking oil (UCO) and poultry fat was converted intocommercially acceptable biodiesel using an FFA stripping FFA refiningprocess followed by transesterification and two biodiesel refiningtechniques: cold filtration using DE and distillation. A sample ofbiodiesel was obtained before cold filtration and distillation tocompare the effectiveness of each method. The biodiesel feedstockmixture was stripped of FFA before entering a base-catalyzedtransesterification process. After being separated from the glycerin andremoving the methanol and water, the dried biodiesel was subjected topurification by either a cold-filtration step using DE or distillationin a wiped-film evaporator. The physical and chemical properties of thebiodiesel before and after purification by cold-filtration ordistillation are provided in Table 6 below. The filtration anddistillation processes both improve the biodiesel quality compared tounpurified dried biodiesel, particularly with respect to cold soakfilterability and sulfur. However, the effect of distillation is morepronounced than cold filtration especially in terms of removing colorcompounds and lowering Acid Number, Cold Soak Filtration time, nitrogenand sulfur.

TABLE 6 Properties of Stripped Used Cooking Oil & Poultry Fat Biodieselwith Cold Filtration or Distillation Stripped UCO/Poultry Fat BiodieselProperties Unpurified Cold Filtered Distilled Wax Reduction (IndirectMethods): Cold Soak Filtration Time 720^(a)   100 78 [ASTM D7501] (s)Turbidity (Nephelometric Turbidity 5.6  3.2 0.5 Unit or NTU) Acid Numberper ASTM D664  0.353 0.346 0.287 Method B (mg KOH/g) Number ofInflection points 1   1 1 Unsaponifiables (wt %)  0.45% 0.36% 0.36%Nitrogen (ppm) 51.3  54.4 24.4 Sulfur (ppm) 12.4  9.4 8.4 Monoglycerides(wt %) 0.29 0.30 0.30 Diglycerides (wt %) 0.09 0.08 <0.005 Triglycerides(wt %) <0.005 0.00 <0.005 Color: Petroleum Products 4   4 0.5 (ASTMD1500) Resemblance to Dyed Diesel no no no ^(a)125 mL out of 300 mLremaining after 720 s

As a result of the high degree of variability in the identity andquantity of impurities found in feedstocks for biodiesel, particularlylow-cost crude feedstocks, a number of process steps as disclosed in theembodiments of the invention may be employed as disclosed herein toconvert highly impure feedstock into high quality and fully acceptablebiodiesel. These various embodiments are described in sufficient detailto enable one of ordinary skill in the art to practice the invention,and it is to be understood that modifications to the various disclosedembodiments may be made by a skilled artisan.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the principles of theinvention. Additionally, certain steps may be performed concurrently ina parallel process when possible, as well as performed sequentially.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

The embodiments, variations, and figures described above provide anindication of the utility and versatility of the present invention.Other embodiments that do not provide all of the features and advantagesset forth herein may also be utilized, without departing from the spiritand scope of the present invention. Such modifications and variationsare considered to be within the scope of the principles of the inventiondefined by the claims.

What is claimed is:
 1. A method for producing a purified biodiesel froma first feedstock comprising: a. removing free fatty acids from saidfirst feedstock to produce a refined feedstock and free fatty acids; b.transesterifying said refined feedstock to produce a first crudebiodiesel; c. distilling said first crude biodiesel to produce thepurified biodiesel and a distillation bottoms; and d. converting thefree fatty acids to a second feedstock using a free fatty acidconversion process.
 2. The method of claim 1, further comprising thestep of using a transesterification process to convert said secondfeedstock to a second crude biodiesel.
 3. The method of claim 2, furthercomprising the step of combining the second crude biodiesel with thefirst crude biodiesel and refining the first crude biodiesel and secondcrude biodiesel together in step (c).
 4. The method of claim 1, furthercomprising the step of combining the second feedstock with the refinedfeedstock and transesterifying the refined feedstock and secondfeedstock together in step (b).
 5. The method of claim 1 furthercomprising the step of pretreating said first feedstock to produce apretreated feedstock before the free fatty acids are removed from saidfirst feedstock and using the pretreated feedstock as the firstfeedstock in step (a).
 6. The method of claim 1, wherein said firstfeedstock contains between about 0.2 wt % and about 30 wt % free fattyacids.
 7. The method of claim 1, wherein said first feedstock comprisesat least one of corn oil, palm oils, fatty acid distillates,distillation bottoms, brown grease, poultry fat, used cooking oil,pennycress oil, algae oil, soybean oil, and canola oil.
 8. The method ofclaim 1, wherein the second feedstock comprises glycerides.
 9. Themethod of claim 1, wherein said purified biodiesel has a lower AcidNumber than the first crude biodiesel.
 10. The method of claim 1,wherein said purified biodiesel has a lighter color than the first crudebiodiesel.
 11. The method of claim 1, wherein said purified biodieselhas a lower wax content than the first crude biodiesel.
 12. The methodof claim 1, wherein said first purified biodiesel has a lower sulfurcontent than the first crude biodiesel.
 13. The method of claim 1,wherein said purified biodiesel has a lower unsaponifiable impuritiescontent than the first crude biodiesel.
 14. The method of claim 1,wherein said purified biodiesel has a wax content of less than 0.1 wt %,an unsaponifiables content of 2 wt % or less, a soap content of 50 ppmor less, a sulfur content of 500 ppm or less, a monoglyceride contentless than 0.6 wt %, a cold soak filtration test result of 360 seconds orless and a lighter color than the first feedstock.
 15. The method ofclaim 1, further comprising the step of utilizing the distillationbottoms as a renewable fuel feedstock.
 16. The method of claim 1,further comprising the step of utilizing the distillation bottoms as afuel.
 17. A method for producing purified biodiesel from a firstfeedstock comprising: a. removing free fatty acids from said firstfeedstock to produce a refined feedstock and free fatty acids; b.transesterifying said refined feedstock to produce a first crudebiodiesel; c. refining said first crude biodiesel to produce a firstpurified biodiesel; and d. converting the free fatty acids to a secondfeedstock using a free fatty acid conversion process.
 18. The method ofclaim 17, wherein said second feedstock is further processed to producea second crude biodiesel.
 19. The method of claim 18, wherein saidsecond crude biodiesel is processed with at least one of the refinedfeedstock and the first crude biodiesel to produce the first purifiedbiodiesel.
 20. The method of claim 17, wherein said first crudebiodiesel is refined via at least one of a distillation process and afiltration process to produce the first purified biodiesel.
 21. Themethod of claim 17, wherein a distillation bottoms are separated fromthe crude biodiesel during the refining step.
 22. The method of claim21, further comprising the step of utilizing the distillation bottoms asa renewable fuel feedstock or a fuel.
 23. The method of claim 17,wherein the second feedstock comprises glycerides.
 24. The method ofclaim 17, wherein said second feedstock is processed with the refinedfeedstock to produce the first crude biodiesel.
 25. A method forproducing a purified biodiesel from a feedstock containing corn oilcomprising: a. refining the feedstock containing corn oil in a freefatty acid stripping process to produce a refined feedstock and a fattyacid distillate; b. transesterifying said refined feedstock to produce acrude biodiesel; c. distilling said crude biodiesel to produce saidpurified biodiesel and a distillation bottoms; and d. utilizing thefatty acid distillate as a renewable fuel feedstock.
 26. The method ofclaim 25, wherein the purified biodiesel has a lighter color than thefeedstock containing corn oil.
 27. The method of claim 25, wherein thepurified biodiesel has a wax content of less than 0.1 wt %, anunsaponifiables content of 2 wt % or less, a soap content of 50 ppm orless, a sulfur content of 500 ppm or less, a monoglyceride content lessthan 0.6 wt %, a cold soak filtration result of 360 seconds or less anda lighter color than the feedstock containing corn oil.
 28. The methodof claim 25, further comprising the step of utilizing the distillationbottoms as a renewable fuel feedstock.
 29. The method of claim 25,further comprising the step of utilizing the distillation bottoms as afuel.